DNA technology, the clinical laboratory, and the future

Glycoprotein IIIA Gene (PIA) Polymorphism and Aspirin Resistance: Is There Any Correlation?

BACKGROUND:

Platelet glycoprotein (GP) IIb/IIIa receptors play an inevitable role in platelet aggregation. The GP IIIa gene is polymorphic ( PIA1/PIA2) and the presence of a PIA2 allele might be associated with an increased risk for acute coronary syndrome (ACS).

OBJECTIVE:

To examine the prevalence of the PIA2 allele in patients with ACS and in subjects with or without aspirin resistance.

METHODS:

The prevalence of the PIA2 allele was assessed in 158 patients with ACS and PIA2 compared with its prevalence in 199 healthy volunteers. The antiplatelet efficacy of aspirin was examined in all patients with ACS, as well as in 69 individuals who had suffered ischemic stroke and in 58 high-risk subjects without any known ischemic vascular events.

RESULTS:

PIA2 prevalence was significantly higher in patients with ACS (59/158) than in the control group (51/199; p < 0.05). Carriers of the PIA2 allele had a significantly higher risk of developing ACS, even after an adjustment to the risk factors (OR 5.74; 95% CI 1.75 to 18.8; p = 0.004). The occurrence of the PIA2 allele was significantly higher among patients with aspirin resistance than in subjects who demonstrated an appropriate response to the drug (allele frequencies, 0.21 vs 0.14; p < 0.05). All patients homozygous for the PIA2 allele had an inadequate platelet response to aspirin.

CONCLUSIONS:

Our results support the hypothesis that carriers of the PIA2 allele might have an increased risk for ACS. PIA2 homozygosity was associated with an inadequate response to aspirin therapy. Our data further suggest that patients with PIA2 allele homozygosity might benefit from antiplatelet therapy based on adenosine diphosphate antagonists throughout secondary treatment for prevention of ACS.

The future of laboratory medicine - a 2014 perspective

Predicting the future is a difficult task. Not surprisingly, there are many examples and assumptions that have proved to be wrong. This review surveys the many predictions, beginning in 1887, about the future of laboratory medicine and its sub-specialties such as clinical chemistry and molecular pathology. It provides a commentary on the accuracy of the predictions and offers opinions on emerging technologies, economic factors and social developments that may play a role in shaping the future of laboratory medicine.

Does glycoprotein IIIa gene (Pl(A)) polymorphism influence clopidogrel resistance? : a study in older patients

BACKGROUND

Clopidogrel is a potent antiplatelet drug used for secondary prevention after ischaemic cardiovascular or cerebrovascular events. In patients with aspirin (acetylsalicylic acid) intolerance or resistance, it is used as monotherapy. Recent data report that Pl(A) polymorphism of the glycoprotein IIIa gene may account for differences in aspirin-induced antiplatelet effects. An increased degree of platelet reactivity was also reported in Pl(A2) carriers compared with Pl(A1/A1) patients after administration of a clopidogrel 300mg loading dose.

OBJECTIVES

The aim of this study was to assess the modulatory effect of the Pl(A2) allele on platelet aggregation in patients taking long-term clopidogrel. M ETHODS: The prevalence of the Pl(A2) allele was assessed in 38 (21 males, 17 females; mean age 63 +/- 13 years) clopidogrel-resistant and 59 (26 males, 33 females; mean age 63 +/- 11 years) clopidogrel-responsive patients. The polymerase chain reaction-restriction fragment length polymorphism method was utilised to evaluate Pl(A) polymorphism. A Carat TX4 optical platelet aggregometer (Carat Diagnostics Ltd, Budapest, Hungary) was used to measure 5 and 10 micromol/L adenosine diphosphate-induced platelet aggregation.

RESULTS

Significantly more patients were taking combination antiplatelet therapy in the clopidogrel-resistant group than in the clopidogrel-responsive group (50% vs 30%, respectively). The prevalence of the Pl(A2) allele did not differ significantly between the two groups (0.09 vs 0.13), even after adjustment for combination therapy and various risk factors.

CONCLUSIONS

Our results show that carriers of the Pl(A2) allele do not have an increased risk of clopidogrel resistance. These findings and data from our previous studies suggest that patients with a Pl(A2) allele homozygosity may benefit from antiplatelet therapy based on clopidogrel rather than aspirin.

Amplified expression profiling of platelet transcriptome reveals changes in arginine metabolic pathways in patients with sickle cell disease

BACKGROUND

In sickle cell disease, ischemia-reperfusion injury and intravascular hemolysis produce endothelial dysfunction and vasculopathy characterized by reduced nitric oxide and arginine bioavailability. Recent functional studies of platelets in patients with sickle cell disease reveal a basally activated state, which suggests that pathological platelet activation may contribute to sickle cell disease vasculopathy.

METHODS AND RESULTS

Studies were therefore undertaken to examine transcriptional signaling pathways in platelets that may be dysregulated in sickle cell disease. We demonstrate and validate in the present study the feasibility of comparative platelet transcriptome studies on clinical samples from single donors by the application of RNA amplification followed by microarray-based analysis of 54,000 probe sets. Data mining an existing microarray database, we identified 220 highly abundant genes in platelets and a subset of 72 relatively platelet-specific genes, defined by >10-fold increased expression compared with the median of other cell types in the database with amplified transcripts. The highly abundant platelet transcripts found in the present study included 82% or 70% of platelet-abundant genes identified in 2 previous gene expression studies on nonamplified mRNA from pooled or apheresis samples, respectively. On comparing the platelet gene expression profiles in 18 patients with sickle cell disease in steady state to those of 12 black control subjects, at a 3-fold cutoff and 5% false-discovery rate, we identified approximately 100 differentially expressed genes, including multiple genes involved in arginine metabolism and redox homeostasis. Further characterization of these pathways with real-time polymerase chain reaction and biochemical assays revealed increased arginase II expression and activity and decreased platelet polyamine levels.

CONCLUSIONS

The present studies suggest a potential pathogenic role for platelet arginase and altered arginine and polyamine metabolism in sickle cell disease and provide a novel framework for the study of disease-specific platelet biology.

Molecular diagnostics of injury and repair responses in critical illness: what is the future of "monitoring" in the intensive care unit?

OBJECTIVE

To identify potential future means of monitoring injury and repair in critical illness.

DESIGN

Review of the literature.

RESULTS

Critically ill patients are monitored extensively and intensively by such means as hemodynamics, laboratory values, and radiologic studies. In general, however, the goal of monitoring has been to measure the degree of injury and to prevent further injury, rather than to measure repair. Measures of repair have been limited to phenotypic end points such as return of organ function, as measured by blood chemistry. In this article, I examine how it may be possible in the future to monitor the progress of repair using genomic and proteomic biomarkers. These types of monitors would enable clinicians to control the healing environment using real time, rapid biomarkers, and sophisticated techniques to target therapy to the patient's current inflammatory state, taking into account the genetic makeup of the patient and his or her likely response to a given drug.

CONCLUSIONS

The rapidly evolving sciences of genomics, proteomics, computational biology, and complex system theory can be used a) to model critical illness; b) to model adaptive and maladaptive responses to critical illness; c) to tailor treatments to create an ideal inflammatory environment for repair and regeneration, taking into account the individual genetic contribution; and d) to monitor the progress of repair. The major obstacles to reaching these goals are technological, and experience suggests that they will be overcome.